Animals have adapted a number of different ways to swim and fly. But new research suggests that wings, fins and flukes share a couple of basic design parameters.

Regardless of size, material or species, flapping appendages all have two things in common, the relative bending location and the maximum bending angle, researchers report the February 18 in Nature Communications.

The results show that, despite staggering variety across species — from long-eared bats to humpback whales — different propulsion methods evolved with the same two criteria. The data may also help engineers design more efficient wings and propellers.